The generalized transducing particles made by the virulent coliphage T1 are being characterized as follows: (a) density, (b) UV sensitivity, (c) dependence on the donor's recA function, (d) time of production, (e) efficiency of transduction, and (f) specificity of the particle's DNA. The transduction of plaque forming lambda from cells lysogenic for lambdoid prophages by T1 is being characterized according to the influence on DNA pick-up and expression of the following: (a) the recA system of E. coli, (b) the red system of lambda, (c) site specific recombination mediated by the int gene of lambda, (d) terminal end formation by the "A" gene of lambda, (e) length of the chromosome of the transduced lambdoid phage, and (f) location of the lambdoid prophage being transduced. The effect of transcription on transduction is being characterized by studying the effect of polar mutations on crossover in the affected region.